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Friday, March 13, 2015

Learning to Identify Lesser and Greater Scaup

***This guest post is written by Brian Zwiebel. Brian is an award-winning photographer that has been published in international books and magazines. One of the many things that makes him a great photographer is his understanding of the identification and behavior of his subjects. If you'd like to learn how to get incredible photographs, join Brian on one of our Sabrewing Nature Tours photography trips.

Thanks to Rob for inviting me to be a guest blogger just as we start one of my favorite times of the year. Waterfowl migration is in full swing so let’s try to answer that age old question: “Is that a Lesser or a Greater Scaup?”

Over the years I have repeatedly heard that head color is a great way to separate the male scaup species; blue for Lesser Scaup (LESC) and green for Greater Scaup (GRSC). There are several problems with this method. First, this does nothing to help us with the females. Second, in poor lighting such as back lighting or heavy overcast, the head will be nearly colorless appearing black even at relatively close range. Lastly, when viewing in good light the green head for male GRSC is quite reliable, however more than 50% of my LESC images show a bird with a green head.

The following images and captions will illustrate a number of other key field marks to consider. Comparison photos will show the Lesser Scaup on left.

Head shape is much more reliable than head color for separating the scaup. Here we have aLESC showing the flat back of the head. GRSC have a much more rounded head. Also notethe nail (black tip) of the bill is quite small on LESC while the black spreads and is muchwider at the tip on a Greater Scaup. The nail size is probably the most consistentlyreliable field mark but unfortunately most birds will be too distant for it to be of much use.

Head shape also works quite well for the female (and immature male) scaup. Note flat backof head on LESC and perfectly rounded head on GRSC. The nail can be even moredifficult to discern on female scaup as it lacks the rich black of the nail found on the males.

Another aspect of head shape to consider is the large jowls or “cheeky” appearance ofthe GRSC. The LESC has a much finer build. This trait is not as easy to see whena bird is in perfect profile as in the first head comparison image.

While we are discussing structure and build of the head, take a look at how broad the billis on this GRSC. The bill tip almost reminds me of the flared nostrils look ofa Northern Shoveler. In comparison the LESC bill is very slight but this is best viewedat close range.

To find a GRSC in a large group of distant LESC it can be useful to quickly scanfor a male bird with exceptionally bright flanks. Male LESC have fine grayvermiculations in the flanks while GRSC vary from pure white or white withminimal gray flecking. This is not a perfect field mark on its own as there is someoverlap depending on molt and age of the birds but it will allow you to quickly focusin on some likely candidates.

Sometimes with the above clues scaup ID can be quite straight forward. Other times we need to rely on the preponderance of the evidence. While weighing the evidence it is good to keep a few additional things in mind.

First, head shape is difficult to judge in flight. This is a LESC showing a green, roundish head.

Second, preening and scratching scaup sometimes roll over on their sides which at adistance will flash what appears to be a very white flank. What may look like a goodindicator for GRSC may in fact be the very white belly of a LESC.

Third, a number of sources mention the length of the white wing stripe as a field markfor scaup in flight. This can be hard to determine even when frozen in a picture at1/2,000th of a second. Here we can see the GRSC wing stripe is quite a bit longer.

Even with quality optics and a great understanding of scaup identification we are sometimes left with no choice but to label a bird as scaup species and there is nothing wrong with that!